Platelet-Derived-Growth-Factor (PDGF), insulin, and vasopressin stimulate sodium ion dependent amino acid uptake into human diploid fibroblast cells in culture. The central hypothesis of this proposal is that the mitogenic hormone, PDGF, which stimulates the proliferation of human cells, regulates amino acid transport by a mechanism which differs from that by which the other hormones operate. PDGF treatment renders the cells competent to synthesize DNA in response of other hormones known as progression factors. The hypothesis suggests that PDGF induces a programed sequence of membrane changes, among which is amino acid transport stimulation, which renders the cells competent. The difference between PDGF stimulated transport and that stimulated by the other hormones will be assessed by a variety of techniques. These include determining whetgher RNA or protein synthesis is necessary for the transport response and what transport kinetic alterations have been induced by hormonal treatment. If the membrane responses to PDGF or the other hormones are stable, then they should be reflected in the transport responses of plasma membrane vesicles isolated from hormone treated cells. Plasma membrane vesicles will be prepared and the properties of the sodium independent transport systems investigated. The role played by possible second messengers, such as cyclic nucleotides and prostaglandins, in the transport response will also be ascertained. Finally the new membrane proteins induced by each hormone will be determined. If PDGF, insulin, and vasopressin do regulate amino acid transport by different mechanism, these mechanisms will be elucidated. If they operate by a common mechanisms, the means by which several different hormones may activate a common regulatory response will be ascertained.